All you need is love. That is the theme song of pro-same-sex marriage proponents. It is the slogan of Louisa Wall, author of the same-sex marriage bill. If two gay people love each other and want to “marry”, why don’t we allow this? But is love enough?

In answering that question, we need to be aware of two other questions: what is marriage? And why is the state involved? The latter question is crucial, because the core issue is one of affirmation, not rights – rights can be dealt with by specific legislation without amending the Marriage Act and upsetting lots of people.

Apart from conveying rights, marriage provides affirmation that the state/society encourages this relationship as a good thing. A crucial question is whether gay relationships are such a good thing as to be endorsed by society as “marriage”.

We should look at the issue of social endorsement through four lenses: love, commitment, health, and society’s interests.

Let’s begin with love. What is “love”? The word covers a raft of sometimes contrary meanings, from sexual desire centred on “my” self-gratification, to heroic self-giving for another. Both heterosexual and same-sex unions may well pass (or fail) this test. The love issue does not debar same-sex marriages.

However, love alone is not enough. It can be fleeting and transient. If marriage is to be serious and not trivial, it needs longevity, buttressed by commitment and faithfulness.

What of gay commitment and faithfulness? Long-term lesbian relationships on average may well be as committed and faithful as that of an average married heterosexual couple. The problem is the gay men.

Some male gay couples are as committed and faithful as typical married heterosexuals. Survey evidence, however, indicates that these are very much a minority.

Significant data on male homosexual behaviour is available through New Zealand Medical Journal articles and the New Zealand Aids Foundation website. The Aids Foundation and the Aids Epidemiology Group at the University of Otago have conducted biennial surveys, the Auckland Gay Periodic Sex Surveys, for the past decade.

The 2010 results covered the sexual behaviour of 1527 gay men in 2008. On the commitment side, the survey indicates that the most common number of sexual partners for gay men over the previous six months was two to five. Just 38.8 per cent of those surveyed had a partner of more than six months’ standing (i.e. relationships with some level of commitment).

However, 52 per cent of these men had also had sex in that period (six months) with other partners. So despite the rhetoric of love and commitment, most male gay couples are not in a genuinely monogamous relationship. Should the meaning of “marriage” be broadened under such circumstances?

There is also the health issue. Male-to-male coupling typically has far greater health risks (because of high levels of anal sex). Both with casual and with “boyfriend” sex the percentage engaging in anal sex is over 80 per cent. Anal sex is never fully safe. Although condoms reduce the risk of sexually transmitted diseases (including HIV/Aids) by around 85-90 per cent, risk remains (because of user misuse or product failure).

Risk is far greater without condom protection. Although 98 per cent of those surveyed knew that anal sex without a condom is very high risk for HIV transmission, 73 per cent did not use a condom at least once in the past six months (the figure for casual sex was 31 per cent).

The result is high levels of sexually transmitted infections amongst gay men. Over 60 per cent of new infectious syphilis cases are gay men. This category also has high rates of gonorrhoea and hepatitis. And 76 per cent of all new HIV diagnoses in 2000-2009 were gay men.

Can we affirm male gay relationships to the level of “marriage”, given the data on faithfulness and health? One can argue change on the basis of “me”, “my rights” and “choice”. But the debate is also about the good of society.

What society needs are stable, faithful, healthy relationships. Stable marriage has gravely weakened in the last generation. There is deep hurt and scarring of many, especially children, as a consequence.

In a direct sense gay “marriage” will not make this worse. Indirectly, however, it will, because it makes marriage, which for many is becoming vague and fuzzy, vaguer and fuzzier still. It is social engineering – with its negative aspects ignored.

We need to have a deep and wide debate, looking at all factors. The same-sex marriage debate is currently far too simplistic. The draft bill is a daft bill.

Laurie Guy is author of Worlds in Collision: The Gay Debate in New Zealand 1960-1986 (Victoria University Press, 2002). He lectures in church history at Auckland University’s school of theology, and also at Carey Baptist College.